Copper is a very soft metal and does not lend itself well to having certain ingredients cooked in it. The lining came about to help preserve the life of the pot and to keep the copper from becoming pitted. Today they are either lined with tin or stainless steel. Tin, allbeit a softer metal like copper and can oxidize just as the copper does, yet it will offer a resistance to higher acid foods and should not pit like the copper. The stainless is self explanitory. Infact the only copper cooking vessels I see any more that are not lined with tin or stainless are the bowl inserts for the KA or the hand mixing bowls. I do have both and are specifically used for egg whites ONLY. I'm sure most of you already know the benefit of the copper when making meringues ;) but for those that don't.... The copper helps to stabilize the egg whites and reduces the need to add cream of tartar, etc. In candy making, they are used specifically for the even heat distribution.
Copper, no matter what the mil thickness, offers all the benefits of the even heat distribution since Copper is the second most conductive metal under 500.00 and ounce. (I believe gold is the first.:crazy:) The main difference comes from whether or not the pot has copper solely on the base or completely covered on all sides. The pans with the base evenly distribute the heat thru the base only. Where as the ones made out of copper and then lined, distribute the heat all the way around the pan. I have noticed a difference when doing reductions. The complete copper pans require less flame to produce the same results as the clad or copper bottoms. Unfortunately pans like the Revereware that only have a thin layer of copper have issue with the copper wearing off after years of use and cleaning.
Also, Pans that are produced using a thicker mil of copper on the outside will last far longer than the thinner ones and will not warp as easily. Unfortunately they do cost BIG$$$$. But they sure do look great.
Also as far as cleaning, in order for the copper to work correctly it must be cleaned frequently. Keeping copper pots and pans sparkley clean is not a vanity issue (although I wouldn't hang a pot in clear view that wasn't
clean:blush:). It is necessary to not create hot spots in the pans.